Laurentiana describes the area around the St. Lawrence River.
Rhizome: short-creeping, covered with old stipe bases, scales tan to light brown, lanceolate, somewhat clathrate.
Frond: 50 cm high by 12 cm wide, deciduous, monomorphic, nearly all fronds fertile, blade/stipe ratio: 3:2.
Stipe: stipes --3 to 8-- clustered at stem apex, grooved, brown at base to straw-colored above, sparsely scaly at base, vascular bundles: 2, round or oblong.
Blade: 2-pinnate-pinnatifid, ovate to lanceolate, usually widest above base, rarely bearing bulblets on the rachis, herbaceous, light green or yellowish-green, sparsely present gland-tipped hairs on rachis and costa.
Pinnae: 12 to 16 pair, perpendicular to the rachis, ± opposite, lanceolate; costae grooves above continuous from rachis to costae; margins serrate; veins free, simple or forked, directed into teeth and notches.
Sori: round, in 1 row between midrib and margin, indusium: cup-shaped, beneath sorus on midrib side, on a vein, sporangia: brown to black, maturity: midsummer to early fall.
Habitat: cracks and ledges on cliffs, often on calcareous substrates .
Distribution: north central North America to northeastern North America, but not boreal, uncommon or pehaps misidentified as C. fragilis.
Hardy to -40°C, USDA Zone 2.
Smaller than C. bulbifera, with brown, not maroon or reddish stipes, blade widest above the base, veins sometimes running to the teeth tips, rarely with bulbils. Larger than C. fragilis, with more pinnae, veins sometimes running to the notches.
Cystopteris fragilis (Linnaeus) Bernhardi var. laurentiana Weatherby